Figure 1. Crosstalk between vesicle trafficking and the unfolded protein response. (A) A block in the secretory pathway can indirectly activate the UPR (dotted arrows) by causing accumulation of proteins in the ER. The UPR, in turn, stimulates the expression of RNAs encoding secretory proteins, and will eventually alleviate the defect in transport. (B) Vesicle trafficking directly regulates the UPR: Ypt1 interacts with unspliced HAC1 and leads to its degradation. A block in Ypt1 function will result in accumulation of HAC1, the RNA will get processed into Hac1 protein and eventually produce enough transcription factor to activate the UPR (solid arrows).